1. Field of the Invention
The present invention relates to the measurement of component parts of a gaseous stream. It particularly relates to the measurement of certain selected constituents of a gas which are present in only trace amounts.
2. Prior Art
In recent years there has been a considerable interest in the quality of our environment, particularly with respect to the effects of air pollution on health. Recent studies have indicated that even trace amounts of certain pollutants could have adverse health effects. For example, recent studies indicate that gaseous ammonia plays a significant role in the formation and stabilization of aerosol particles in a polluted atmosphere, and these particles can potentially cause adverse health effects. Ambient ammonia generally is present in the atmosphere in the parts per billion range. While there are numerous methods for measuring ammonia, most existing methods are not sufficiently sensitive to measure ambient ammonia at such low concentrations or are not amenable to continuous monitoring.
There are, for example, wet chemical methods of measuring ammonia which utilize established techniques and relatively inexpensive hardware. However, wet chemical methods are subject to strong negative interference from formaldehyde, which is known to be present in the atmosphere in concentrations equal to or exceeding the nominal ammonia concentration. Attempts to minimize such interference have not been altogether satisfactory. In addition, wet chemical methods are not suitable for real time analysis or continuous monitoring.
The spectroscopic technique provides for direct measurement in real time. However, this technique is subject to strong interference by the presence of other constituents which also are present in the atmosphere, frequently in greater concentrations than, for example, ammonia. In addition, to obtain reliable analysis in the low parts per billion concentration requires a skilled technician. Another disadvantage is that the equipment is expensive.
Another potential method for ammonia measurement is chemiluminescence. The chemiluminescence method relies on measuring ammonia by converting it to nitrogen oxide. However, the ambient nitrogen oxide concentration is much larger than the ambient ammonia concentration. The accuracy and reliability of this method, therefore, is limited and strongly influenced by small fluctuations in the ambient nitrogen oxide concentration.
Obviously, there is a need for an improved method for determining the concentration of trace constituents in a gaseous stream such as ambient air.